difficult to explain by words...it is some kind of experience; use any opportunity to look at contaminated cultures of colleagues (even experienced scientist have sometimes to struggle with contamination);

install a routine protocol to check cell cultures for at least mycoplasm contamination

Contaminated cell culture will be cloudy, and have a rapid medium color change, e.g from red to yellow in 1 day. If you view under the microscope, you can see the bacteria moving around in the medium - not a pleasant sight I tell you. If you're not sure, you should test for contamination either by inoculation of the cell culture medium into broth (LB, BHIB, etc) or spread it on a non-selective agar plate. You can also place a dish of media in the incubator and leave it for a few days to a week, to see whether your media is free of contaminants. Mycoplasma detection should be done every 3 months, and there are a number of ways you can do this, the most common and sensitive being the PCR-based method. You can easily get kits from a known manufacturer.

Contaminated cell culture will be cloudy, and have a rapid medium color change, e.g from red to yellow in 1 day. If you view under the microscope, you can see the bacteria moving around in the medium - not a pleasant sight I tell you. If you're not sure, you should test for contamination either by inoculation of the cell culture medium into broth (LB, BHIB, etc) or spread it on a non-selective agar plate. You can also place a dish of media in the incubator and leave it for a few days to a week, to see whether your media is free of contaminants. Mycoplasma detection should be done every 3 months, and there are a number of ways you can do this, the most common and sensitive being the PCR-based method. You can easily get kits from a known manufacturer.

Good luck!

"the most common and sensitive being the PCR-based method"

This is factually incorrect......please check out the ATCC or HPA website. I have put the HPA link below!!!!!!!

This should be common knowledge and I am suprised that anyone with Cell Culture experience does not know this. The ATCC, the WORLD'S largest commercial supplier of cells, NO LONGER USE PCR AS A METHOD FOR MYCOPLASMA DETECTION....BECAUSE IT IS SO UNRELIABLE.